A site could do it either way. Having a category for them makes it easier to find them all, and they’d usually share tags with main.
Responses to your meta list:
Yes, each category can have CSS. Codidact would offer some standard themes and suggested associations (use the gray theme for meta, people tend to use the blue theme for wikis/canonicals/etc, that sort of thing).
Yes, covered in the spec already. A category can have its own tag set or share.
Frame challenge: one profile page, and when you visit it from a category the filter to show that category’s stuff is auto-applied. (But you can then choose other filters to move among categories if you like, and maybe we even give you an “all” tab.)
Ditto: search should automatically filter to the current category by default. If you want to search the entire site (all categories), that requires some sort of explicit action TBD.
No queues yet, but yes reviews need to be separate. I think that can still be one queue and an auto-filter, though. Or if that’s not practical, then maybe queues, like tag sets, are separable. That’s a decision for later when we get to the review mechanism (which could well be just a list of stuff on one page and not something like the SE queue – who knows?).
Good point. Close reasons, like tag sets, should be able to be category-specific. (I’m going to say not MVP here, as for MVP I think we’re creating about three close reasons and “other” + textbox.)
We need to be thoughtful about navigation, yes. I think we can be but we don’t have mockups yet.